The present invention relates to a photosensitive resin composition, and more particularly a photosensitive composition which is superior in chemical resistance for developer, resolution, sandblasting resistance, and stability, and is suitable for use in dry film resist.
A laminated film with three layers, in which a photosensitive resin composition is applied on a base film such as a polyester film, dried and formed as a layer, and a protective film such as a polyethylene film or a polyvinylalcohol film is stacked thereon, is generally referred to as a dry film photoresist (hereinafter, referred to as DFR). The film has been widely used in manufacturing processes for printed circuit boards, precision machining processes for metals, etc.
Upon application of such a film, first, either the base film or the protective film, which exhibits the weaker adhesion, is separated and removed from the DFR, and the side bearing the photosensitive resin composition layer is affixed onto the surface of a base substrate, such as a copper surface of a copper laminated substrate, on which a pattern is to be formed. Then this is subjected to exposure with a pattern mask being in contact with the film on the other side (in some cases, exposure is applied after the film on the other side has been removed). And the other film is separated and removed, and then subjected to a developing process. As for developing systems after exposure, there are those of the solvent-developing type and the diluted alkali developing type.
Besides DFRs, another method has been well-known, in which a photosensitive resin composition is directly applied on the surface of a base substrate and formed as a film, and a pattern mask is made in contact therewith, with a film such as a polyester film interpolated in between, and then exposure is applied thereto.
In recent years, a sandblast method using a DFR has been used for forming a barrier rib in a plasma display panel, etc.
With respect to photosensitive resin compositions for DFRs used in such applications, the following compositions are, for example, listed: (1) a solid-state photo-polymerizable resin composition comprising a polymerizable crosslinking unsaturated acrylic urethane compound having an acid number in the range of 20 to 200 mgKOH/g prepared by a particular method, an alkali-soluble high polymer composition having a compatibility with the urethane compound, and a light sensitizer (Japanese Examined Patent Publication No. 924/1987 (Tokukousho 62-924)), (2) a photosensitive resin composition using a urethane prepolymer having a particular carboxyl-acrylic type terminal (Japanese Examined Patent Publication No. 10165/1990 (Tokukouhei 2-10165)), (3) a photo-polymerizable composition comprising a base polymer having an acid number in the range of 100 to 600 mgKOH/g and the average molecular weight in the range of 10000 to 500000, a polymerizable unsaturated compound containing 10 to 50% by weight of a compound having one polymerizable unsaturated group and 10 to 90% by weight of a compound having two polymerizable unsaturated groups, and a photo-polymerization initiator (Japanese Unexamined Patent Publication No. 6202/1991 (Tokukaihei 3-6202)), (4) a photosensitive resin composition containing specific amounts of the respective materials of a base polymer having an acid number in the range of 100 to 200 mg KOH/g and the average molecular weight in the range of 30000 to 120000, an ethylenically unsaturated compound, P,P'-bis(dialkylamino)benzophenone, hexaarylbiimidazole and a leuco dye, and also containing not less than 95% by weight of an ethylenically unsaturated compound having two polymerizable unsaturated groups in its compounds (Japanese Unexamined Patent Publication No. 248621/1995 (Tokukaihei 7-248621), (5) a photosensitive polymer composition containing a particular polymer having a carboxyl group and an amide bond, an unsaturated compound containing an amino group or its quaternary salt and 4,4'-diazide-3,3'-dimethoxybiphenyl (Japanese Unexamined Patent Publication No.219224/1995 (Tokukaihei 7-219224), (6) a photosensitive resin composition comprising a urethane compound containing a specific (meth)acrylate group terminal, an alkali-soluble high polymer compound having an acid number in the range of 50 to 250 mgKOH/g and a photo polymerization initiator (Japanese Unexamined Patent Publication No. 305017/1996 (Tokukaihei 8-305017)), (7) a photosensitive resin composition comprising a urethane(meth)acrylate compound modified with a carboxyl group that has not less than two (meth) acryloyl groups, an acid number in the range of 50 to 250 mgKOH/g, and Tg after cure in the range of 5 to 95.degree. C., an alkali-soluble high polymer compound having an acid number in the range of 50 to 250 mgKOH/g and a photo-polymerization initiator (Japanese Unexamined Patent Publication No. 54734/1996 (Tokukaihei 8-54734), (8) a photosensitive resin composition comprising a urethane (meth)acrylate compound containing not less than two acryloyl groups, an alkali-soluble high polymer compound having an acid number in the range of 50 to 250 mgKOH/g, a high polymer compound having a thiocyanic alkali salt and a poly(alkylene oxide) segment, and a photo-polymerization initiator (Japanese Unexamined Patent Publication No. 152713/1997 (Tokukaihei 9-152713).
However, in the sandblast method, the following properties are required: chemical resistance for developer (fine line adhesion after development), sandblasting resistance (fine line adhesion after sandblasting), and stability in forming DFRs (changes in color tones, deterioration in resolution and adhesion, etc.) and so on. In the case of the above-mentioned (1), (6), (7) and (8), the sandblasting resistance comparatively satisfied, but these pose problems in alkali property cause an insufficient resolution, and require a strict management in the density of a developing liquid and developing time upon developing (narrower latitude). In the case of the above-mentioned (2), (3) and (4), the resolution and chemical resistance for developer are comparatively satisfied, but the sandblasting resistance is insufficient. In (3) and (4) the resist after cure is not flexible, and the sandblasting resistance is insufficient. In (5), the resolution is not sufficient, the stability of the photo dope (a solution of photosensitive resin composition) and DFRs using it is insufficient, and the sandblasting resistance is inferior; therefore, more improvements are required to apply it to the sandblast method.
Moreover, in the sandblasting of SiC substrates which requires blasting powder with high hardness at high pressure, none of the above-mentioned resin compositions are successfully applied to practical use, and resin compositions for DFRs having a higher sandblasting resistance have been demanded.